Yeast chromosomal DNAs contain terminal interstrand cross-links. Specific fragments containing cross-links will be analyzed with enzyme probes to test the notion that a terminus has a hairpin structure. Terminal sequences will be cloned and the clones used to map this telomere DNA, to look for relatedness between different telomeres and to probe the nucleotprotein organization of the telomere. The timing and topology of telomere DNA replication will be examined using hybridization probes and electron microscopy. Control of the activation of replication origins in yeast will be studied. The 2 microns DNA plasmid will be examined for alterations associated with origin activation and its refractoriness to secondary activation. The replication of new yeast plasmids, formed from chromosomal DNA segments, will be examined to determine the extent to which their origins remain under normal replication controls. These plasmids will also be used as hybridization probes in cell synchrony and dense isotope transfer experiments to measure the temporal program of origin activation under different growth conditions. The quantitative transmission of different yeast multiple copy genetic elements through yeast meiosis and sporulation will be determined using radiolabel, dense isotope experiments. These experiments will include an assessment of the possibility that double strand RNA-containing virus-like particles are transmitted as intact structures. In addition, the general mechanism of double strand RNA replication will be determined.